A separator for an electrochemical battery refers to an intermediate membrane segregating a cathode and an anode from each other in a battery, while continuously maintaining ion conductivity, thereby allowing battery charging and discharging.
Recently, along with weight lightening and miniaturization trend of an electrochemical battery for high portability of an electronic device, a battery is also required to have high power and large capacity in order to be used for an electric car, and the like. Thus, a separator for a battery is required to be thin and have light weight, and at the same time, to have excellent thermal shape stability for production of a high power battery.
Particularly, in case where a polyolefin-based film is used as a substrate film of the separator, the film may melt down even at relatively low temperature, and thus, in order to compensate for such a problem, a study to improve the thermal resistance of the substrate film has proceeded. It is suggested in Korean Patent Registration No. 10-0775310, etc. that a coating layer of a mixture of organic and inorganic materials is formed on one or both surfaces of a substrate film of a separator, in order to improve the thermal resistance of a substrate film.
Meanwhile, an attempt has been made to improve thermal stability of a coating layer, by using an organic binder having excellent thermal resistance such as polyimide as a coating agent component of a separator. However, the organic binder having high thermal resistance generally does not dissolve in a low boiling point solvent, which later causes a problem of being properly unable to performing a drying process of the solvent after coating a separator. Moreover, this not only decreases air permeability of a separator, but also reduces compatibility with other coating agent components added together so as to make it difficult to be substantially utilized as a coating agent.
Therefore, the development of a coating agent which has excellent thermal resistance, is easily prepared, and also has excellent drying processability, is needed.